Polyethylene terephthalate, commonly called PET, is a particular thermoplastic, widely used in plastic bottles and thus something that society wants to recycle. PET is used in bottles for its special properties, for instance, for containing carbonated beverages and being chemically non-reactive to the beverages. When used in fibers, the same PET material is often commonly called polyester.
The present invention relates in part to the technology for using recycled and virgin PET in products which would otherwise be wholly made of polyethylene (PE) or polypropylene (PP). There are variances in supply and cost amongst recycled plastic raw materials; and, in that context it is attractive to use PET for structural items such as molded plastic leaching chambers and storm chambers. A historic problem is that the properties of recycled thermoplastics tend in general to be inferior to virgin materials. Nonetheless, it would be desirable to make products, in particular leaching chambers and other arch shape cross section chambers having perforated sidewalls from recycled PET, alternatively from virgin PET, for the benefit of better mechanical properties such as impact resistance than are provided by some other common plastics used in leaching chambers, such as polypropylene PP and polyethylene PE.
Leaching chambers of PP and PE have heretofore been made by methods which include thermoforming of sheet and injection molding. While a disadvantage of injection molding is the cost of molds and molding equipment, injection molding has been desirable because it provides precise wall thicknesses compared to thermoforming and does not require a secondary operation to make sidewall perforations. Recycled PET presents problems to injection molding, particularly with respect to flowing the plastic and filling small channels of an injection molding mold.
Leaching chambers made by thermoforming have been heretofore marketed with cut hole perforations in the sidewalls. A thermoformed leaching chamber made of PP or PE might have a wall thickness which varies between 0.08 inch and 0.16 inch. To use such chambers in common soil including sandy soil, they have to be covered with geotextile, otherwise soil will migrate to the interior of the chamber through the sidewall holes.
In comparison injection molded chambers have sidewall slots and associated louvers, and they present less need for geotextile, along with a more desirable exposure of the soil at the opening in the sidewall of the chamber. During use, leaching chambers are buried in soil and it is desirable to inhibit any tendency of the surrounding soil to enter the chamber interior through the sidewalls. Thus, the configuration of slotted sidewalls has varied over time in commercial products as has been described in patent literature. Generally, the slots are defined vertically by spaced apart horizontal louvers which typically have smooth underside and topside surfaces. Typically, the louvers have wedge shape cross sections. Sometimes, the louvers of injection molded leaching chambers have a lip or ridge at the innermost edge of the top surface of a louver. See for instance, Birchler et al. Pat. Pub. 20070077122 and England U.S. Pat. No. 7,207,767.